1. Field of the Invention
The present invention relates to an inner frame and a case unit.
2. Description of the Related Art
In a conventional case unit for use in an electronic device such as a wristwatch, etc, when a module member which holds various parts therein is incorporated into a case member as an outer case, an inner frame is disposed between the case member and the module member in order to prevent the module member from moving in the case member, so that the module member held in the module member is positioned and secured in a predetermined position in the case member.
For example, Japanese patent application KOKAI publication No. 2007-132771 discloses a timepiece which comprises a timepiece module and a body case housing the timepiece module, and which has a structure by which a inner frame as a pressing member is arranged for positioning and pressing the timepiece module in the body case.
In the past, in order to secure the inner frame to the case member without being rattling, one of the following constructions is employed, by which the inner frame is formed to set its outer diameter to be substantially equal to a diameter of an inner periphery of the case, projecting portions are provided on an outer side surface of the inner frame not to provide a gap between the inner frame and the case member, and the inner frame is press fitted into the case member.
However, in a case that the inner frame is made of plastic to increase its close fit to the module member and to the case member and the case member is made of a hard material such as metal, when the inner frame is pressed-into the case member, the outer surface of the inner frame is scraped off by friction generated between the outer surface of the inner frame and the inside surface of the case member, thereby producing shavings.
Especially, in a structure in which a cover member is threaded into an opening portion of the case member to cover the opening portion, when the inner frame is press-fitted into the case member, there is a large possibility that the inner frame contacts a threaded portion formed on an inner periphery of the opening portion of the case member and is scraped off.
For example, in a wristwatch, shavings produced from the inner frame may fall into a clearance between a front glass cover and a liquid crystal panel and/or onto electronic parts, thereby producing troubles.
If the diameter of the inner frame is set small than the inner diameter of the case member, the inner frame is prevented from being in contact with the case member and from being scraped by the case. But, the inner frame holding the module member may move within the case body and may be rattled. Thus, there is a need to provide a member such as a spacer to secure the inner frame, and it increases the number of parts and that of manufacturing steps. Finally, a manufacturing cost is increased.
The present invention is derived from the above described circumstances, and has an object to provide an inner frame with a simple structure which can prevent the inner frame from being scraped off by the case member even if it contacts the case member and which can secure the module member within the case, and a case unit.